1. Field of the Invention
This invention relates to a process and apparatus for introducing solid particulates into highly pressurized fluid streams to produce a high pressure particulate containing fluid jet which is suitable for many cutting and cleaning applications.
2. Description of the Prior Art
Fluid jets are commonly generated by pressurizing fluids with a suitable pump and ejecting the pressurized fluid through a nozzle means. The water jets thus generated are useful for a wide range of applications, such as sprinkling lawns, extinguishing fires, and mining minerals. Currently, water jets generated at pressures up to 20,000 psi are routinely used in industrial cleaning, such as removing scales and deposits in exchange tubes and reactors. Water jets generated at pressures of up to 60,000 psi are used industrially to cut various materials, such as paper products, leather, polymers, plastics, textiles and asbestos products. Utilizing high pressure water jets for cutting operations is gaining popularity because of its many inherent advantages, including absence of tool contact and wear, heat and dust generation, and high speed and quality of cuts. Furthermore, the present emphasis on energy consumption and efficiency encourages the development of improved tools and methods for cutting hard materials.
The water jet cutting method has not been used widely primarily because of high equipment costs resulting from the high fluid pressure involved, high energy consumption, and the inability to cleanly cut very hard materials, such as concrete, rock, glass, hard plastics, and metals. Increasing the water pressure and thus the power input to a very high level, does not improve the quality of the cut in proportion to the costs incurred. The application of high pressure water jets to cut rock and concrete has been discussed in many publications, including: L. H. McCurrich and R. D. Browne, "Application of Water Jet Cutting Technology to Cement Grouts and Concrete"; Paper G-7, 1st International Symposium on Jet Cutting Technology, Coventry, U.K., April 1972; A. G. Norsworthy, U. H. Mohaupt and D. J. Burns, "Concrete Slotting with Continuous Water Jets at Pressures up to 483 MPa", Paper G-3, 2nd International Symposium on Jet Cutting Technology, Cambridge, U.K., April 1974; and T. J. Labus and J. A. Hilaris, "Highway Maintenance Application of Jet Cutting Technology", Paper G-1, 4th International Symposium on Jet Cutting Technology, Canterbury, U.K., April, 1978. A high pressure pulsed water jet apparatus and process is taught by U.S. Pat. No. 4,074,858.
Particulate streams comprising abrasive particles propelled by compressed air have been used to cut and/or abrade many hard materials. This particulate containing stream is quite effective when the abrasive particles are accelerated to a high velocity and ejected through a suitable nozzle. The difficulty in containing the particles and dust generated during the cutting operation, however, prohibits the large industrial scale use of particulate containing air jets.
The combination of solid particulates with a high pressure fluid jet has been utilized for several purposes. For example, U.S. Pat. No. 2,821,396 teaches solid particles in an air or steam injector as an attrition impact pulverizer; U.S. Pat. No. 3,424,386 teaches mixing of granular solids with a liquid for use in sandblasting; U.S. Pat. Nos. 3,972,150 and 3,994,097 teach water jets having particulate abrasives for cleaning with water pressures under 5000 psi; U.S. Pat. No. 4,080,762 teaches a fluid and abrasive jet for paint removal with fluid pressures up to 30,000 psi; and U.S. Pat. No. 4,125,969 teaches a wet abrasion blast cleaning apparatus and method utilizing soluble abrasive materials. U.S. Pat. No. 4,449,332 teaches a nozzle holder for dispensing a water jet containing particulate abrasive material which may be used for cutting or cleaning applications. The nozzle assembly is capable of withstanding high liquid pressures of between about 10,000 to about 50,000 psi.
U.S. Pat. No. 4,478,368 teaches a high velocity particulate containing fluid jet apparatus and process providing improved fluid jet quality by utilizing multiple fluid jets and flow shaping construction. This patent also teaches the supply of solid particulates in a foam for mixture with the fluid jet stream to minimize energy loss of the fluid jet stream and provide better control of the introduction of solid particulates into the fluid stream. Very hard materials, such as concrete, rock, glass and metals, may be cut using fluid jets containing abrasive particulates which have been generated at fluid pressures of up to 60,000 psi. For example, glass can be cut into complicated shapes with abrasive fluid jets when very hard abrasives, such as garnets, are used. Fluid jets containing abrasive particulates may be utilized to make many different types of cuts. The kerf produced by a suitable abrasive water jet nozzle may be as narrow as less than 0.05 inch or as wide as more than 1.0 inch.
In these types of particulate containing fluid jet generators, the factor which determines the cutting capabilities of the abrasive fluid jet is the efficiency of the nozzle assembly in accelerating the particulates in the fluid jet for cutting applications. It is desirable that the velocity of the abrasive fluid jet as it exits the nozzle is as high as possible, and that all particulates introduced be accelerated to a very high speed. It is preferred, in these types of abrasive fluid jet generators, that all fluid and particulate chamber walls have smooth surfaces to minimize fluid turbulence. Mixing of abrasive particulates into a highly pressurized, coherent fluid jet is very difficult to achieve.
There are also applications in which it is desirable for the particulate containing fluid jet to provide uniform particulate dispersal over a relatively large surface area. Such applications include cleaning of large surface areas and spraying to disperse a solid particulate agent, such as solid insecticides. In these types of applications, it is desirable that the particulates accelerated in the fluid jet be distributed uniformly and evenly over a large surface area. Currently available fluid jet nozzles used for sandblasting, ship hull cleaning, and other blasting applications, are deficient both in terms of speed of application and uniformity of particulate distribution. Large quantities of particulates are consumed unnecessarily in such blasting operations.